The present invention concerns compositions for the permanent shaping of hair containing a mercaptoethylamine and/or one of its salt as keratin reducing agent and to a method for permanent shaping of hair using these compositions.
The well-known classical technique for performing a permanent shaping of hair is based on two treatment steps. In the first step the cystine-disulfide bridges of the hair keratin are opened by action of a composition (shaping composition) containing a reducing agent. Then the hair is put in the desired shape. In a second step cystine-disulfide bridges are again closed using a fixing composition, i.e. a composition containing an oxidizing agent.
Thioglycolic acid, for example as its ammonium or monoethanolamine salt, is employed as a classic permanent wave reducing agent, as shown by the German Pioneer Patents 948 186 and 972 424. Additional conventional reducing agents include inorganic sulfites, 2-mercaptopropionic acid(thiolactic acid), 3-mercaptopropionic acid, certain mercaptocarboxylic acid esters, cysteine and derivatives of these compounds.
These reducing agents however have a series of disadvantages. In spite of their sufficient action alkaline preparations based on mercaptocarboxylic acids produce hair damage, which manifests itself in multiple hair strand breaks. Many times these compositions also load the scalp skin in an undesirable manner.
Finally an intensive perfuming of the product is subsequently required because of the unpleasant smell of the reducing agent used. One can solve several of the above-mentioned problems by using 2-mercaptopropionic acid(thiolactic acid). Generally the thiolactic acid is characterized by a weaker shaping action than the generally used thioglycolic acid.
The mercaptocarboxylic acid esters, which allow hair shaping also at lower pH values, are not satisfactory in regard to their skin compatibility and their sensitization risk. Instead of the mercaptocarboxylic acid esters mercaptocarboxylic acid amides, such as thioglycolic acid amide or alkyl- and/or hydroxyalkyl-substituted amides, have also been used. These latter compounds are disclosed in International Patent Application WO-A-91/10421 and European Patent Application EP-A-0 455 457. These materials have, a comparatively good shaping power also at reduced pH values, like the carboxylic acid esters, however are still more criticized than the esters in regard to their sensitizing action. Mercaptoethylamines and their salts, in which the nitrogen atom is substituted with two equal straight or branched chain alkyl groups having from 1 to 6 carbon atoms, are already disclosed in German Patent Application 195 03 131.